0194 Sleep Regularity During Extreme Shiftwork is Important for Mood and Subjective Sleep Quality

Abstract Introduction Maritime defence watchstanders adhere to demanding shiftwork schedules (“watchbills”) for extended periods at sea which can pose a challenge to sleep and wellbeing. previous research examining the impact of different watchbill configurations on sleep have relied on sleep duration. Findings have highlighted insufficient sleep during watchstanding but have mixed results when comparing across watchbills. Sleep regularity is important dimension of sleep that has been rarely assessed in shiftworking populations but presents a potential new metric that could help inform watchbill selection. This study investigated sleep regularity assessment as a tool for evaluating watchbills, using a recently introduced metric – the Sleep Regularity Index (SRI). Methods Wrist-worn actigraphy-derived sleep was assessed in Navy active-duty sailors during underway for ~8 days. (Study 1) N=218 sailors from five groups (3hr-on/9hr-off 3/9, 6/18, 7/5/5/7, and 5/15 watchstanders, and dayworkers) were compared based on SRI using Kruskal-Wallis tests. (Study 2) N=24 sailors stood watch on the 5/10, then the 3/9 ~four months later. Performance was assessed using 3-min psychomotor vigilance task (PVT) throughout both underway periods. Subjective sleepiness, sleep quality, and mood were assessed at the end of underway using the Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI) and Profile of Mood States (POMS), respectively. Partial correlation analysis was used to examine the relationship of sleep and SRI to ESS, PVT, POMS, and PSQI. Results (Study 1) Daily sleep duration was non-significantly different between watchbills (all p 0.05). SRI score was significantly lower for the 5/15 watchbill (43.33, IQR = 10) compared to all other watchbills (all p 0.001). (Study 2) Independent of watchbill, SRI score was associated with PSQI (Spearmans rho rs = -.326) and POMS (rs = -.361) score, but not PVT or ESS score (all p 0.05). Daily sleep duration was associated with only ESS score (rs = -.353). Conclusion The SRI is a useful new tool for examining sleep regularity across different shiftwork schedules. Sleep duration and regularity are both important dimensions of sleep to be considered with shiftwork schedules and those which protect both are optimal. Support (if any)